In a steel pipe producing process, a large number of steel pipes having the same specifications (such as a size and a material) are often produced at the same timing. Therefore, usually in a method for managing the production history information (including inspection result) in each production process, a predetermined number of steel pipes having the same specifications are set to a lot as a unit, and management is performed with a sheet in which the production history information is written for each lot. In this management method, the production history information on each steel pipe is not managed, or a number is directly manually written on the steel pipe in order to identify each steel pipe in the lot and the management is performed by writing the production history information associated with the number assigned to each steel pipe in the sheet.
Recently, for Oil Country Tubular Goods (OCTG) which are ones of applications of steel pipes, because OCTG are used under severe conditions, required specifications such as corrosion resistance have become strict. Therefore, for a steel pipe whose required specifications are strict, it is strongly desired that the production history information be properly managed for each steel pipe.
However, in the method for manually writing the number on the steel pipe, there is inevitably a risk of generating a clerical error because an operator manually writes the number, and there is also a risk of incorrectly reading the number because the operator visually reads the number. Furthermore, there is a risk that the number may become illegible because the number written on the steel pipe is erased in conveying the steel pipe in each production process. Therefore, the obtained production history information may be associated not with the corresponding original steel pipe but with another steel pipe, which may result in inability to properly manage the production history information. Accordingly, the steel pipe which does not satisfy the required specifications is mixed and delivered to a customer, which possibly results in, e.g., occurrence of an accident that brings a serious damage to the customer. In addition to the improper management of the production history information, because the operator manually writes the number and visually reads the number, there is a problem that an excessive man-hour is required to manage the production history information.
In order to solve the above problems, there is proposed a method in which, a number (electric number) is automatically assigned according to the conveyance order of the steel pipe by using a process computer for controlling each of production facilities provided in a steel pipe production line or means for detecting the steel pipe conveyed to each of the production facilities, and the process computer manages the number and the production history information while associating them with each other.
However, the steel pipe production process usually includes a process which is performed off-line while the steel pipe is taken out from the production line (on-line). For example, when the result of a steel pipe inspection process in the production line is defective, the defective steel pipe is taken out from the production line, and cutting of end portions of the steel pipe, treatment of outer and inner surfaces of the steel pipe, straightening and the like are performed. When the steel pipe is taken out from the production line, the process computer cannot manage the production history information on the steel pipe taken out based on the number assigned to the steel pipe in the conveyance order.